Flame propagation through zirconium particles coated with different ratios of Fe3O4

• Flame propagated more quickly in zirconium particles coated with an Fe3O4 ratio of 9:1.
• The temperature of zirconium particles coated with an Fe3O4 ratio of 9:1 was higher.
• A replacement reaction occurred between Zr and Fe3O4.

This study investigated the effects of Fe3O4 coating ratios on the characteristics of flame propagation in dust clouds of 38-μm zirconium particles. A high-speed observation system, fine thermocouples, scanning electron microscopy and X-ray photoelectron spectroscopy were used to reveal the flame propagation behaviors, velocities, temperatures and reaction mechanisms in detail. The results showed that the propagating flames emitted a strong white light, with a thin yellow light zone gradually appearing in front of the white light zone. As the concentration was increased, the flame propagation velocities of zirconium particles coated with an Fe3O4 ratio of 9:1 were greater than those of zirconium particles coated with an Fe3O4 ratio of 3:1 due to the zirconium content and the contact area between zirconium particles and the oxygen. The temperatures of zirconium particles coated with an Fe3O4 ratio of 9:1 and zirconium particles coated with an Fe3O4 ratio of 3:1 did not peak in the experimental range. But the temperatures of zirconium particles coated with an Fe3O4 ratio of 9:1 were always higher than those of zirconium particles coated with an Fe3O4 ratio of 3:1. The scanning electron microscopy and X-ray photoelectron spectroscopy demonstrated that a replacement reaction occurred between Zr and Fe3O4 during the combustion process.